U.S. patent number 6,353,791 [Application Number 09/564,776] was granted by the patent office on 2002-03-05 for apparatus and method for determining engine static timing errors and overall system bandwidth.
This patent grant is currently assigned to Cummins, Inc.. Invention is credited to Donald J. Benson, John T. Carroll, III, Taner Tuken.
United States Patent |
6,353,791 |
Tuken , et al. |
March 5, 2002 |
**Please see images for:
( Certificate of Correction ) ** |
Apparatus and method for determining engine static timing errors
and overall system bandwidth
Abstract
A strategy for quantifying and compensating for between-engine
variations in engine static timing, fuel pump phasing and overall
system bandwidth includes a control circuit operable to manage a
fuel control system including a high pressure, cyclically operable
fuel pump and at least one fuel injector operable to supply fuel to
an internal combustion engine from a fuel collection unit. In one
embodiment, the strategy of the present invention is operable to
determine peak values of the fuel pressure within fuel collection
unit and corresponding engine position values for a number of
different engine speeds and solve a corresponding model-based
system of equations to determine a combined engine static timing
and fuel pump phasing error as well as a first overall system
bandwidth value. In another embodiment, the strategy of the present
invention is operable to determine peak values of the pressure
within a combustion chamber of the engine along with associated
engine position values for a number of different engine speeds and
solve for the engine static timing error alone and/or a second
overall system bandwidth value. In yet another embodiment, the two
foregoing strategies may be combined to produce separately the
first and second bandwidth values as well as the individual engine
static timing and fuel pump phasing error values. In any case, the
computed error and bandwidth values may be used to improve the
accuracy of sampled engine and/or fuel control system parameters as
they relate to engine position.
Inventors: |
Tuken; Taner (Columbus, IN),
Benson; Donald J. (Columbus, IN), Carroll, III; John T.
(Columbus, IN) |
Assignee: |
Cummins, Inc. (Columbus,
IN)
|
Family
ID: |
24255837 |
Appl.
No.: |
09/564,776 |
Filed: |
May 4, 2000 |
Current U.S.
Class: |
701/114; 123/447;
123/501; 701/105 |
Current CPC
Class: |
F02D
35/023 (20130101); F02D 41/009 (20130101); F02D
41/3809 (20130101); F02D 2200/0602 (20130101) |
Current International
Class: |
F02D
35/02 (20060101); F02D 41/38 (20060101); F02D
41/34 (20060101); F02M 045/12 (); G05D 001/00 ();
G06F 017/00 () |
Field of
Search: |
;123/445,446,447,456,467,501,502,503,478,480
;701/103,104,105,114,115 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Wolfe; Willis R.
Attorney, Agent or Firm: Barnes & Thornburg
Claims
What is claimed is:
1. Apparatus for determining errors in monitored operating
parameters of a fuel system for an internal combustion engine,
comprising:
means for sensing a pressure associated with a fuel system of an
internal combustion engine and producing a pressure signal
corresponding thereto, said pressure signal having peak values
corresponding to peak pressure values thereof;
means for determining a reference position of said internal
combustion engine and producing a reference position signal
corresponding thereto;
means for determining first and second engine positions at which
peak values of said pressure signal occur for at least first and
second engine speeds; and
means for determining a first operating parameter error value as a
function of said first and second engine positions relative to said
reference engine position.
2. The apparatus of claim 1 further including means for correcting
said pressure signal relative to said reference position signal
based on said first and second operating parameter error
values.
3. The apparatus of claim 1 further including means responsive to
said pressure signal for determining peak pressures of said
pressure signal and associated engine positions.
4. The apparatus of claim 3 further including means for sensing
rotational speed of said engine and producing an engine speed
signal corresponding thereto;
and wherein said means for determining first and second engine
positions is responsive to said engine speed signal to determine
said first engine position when said engine speed signal
corresponds to said first engine speed and to determine said second
engine position when said engine speed signal corresponds to said
second engine speed.
5. The apparatus of claim 4 wherein said means for determining a
reference position of said engine is operable to determine said
reference position as an engine position corresponding to a top
dead center (TDC) position associated with a fuel pump of said fuel
system.
6. The apparatus of claim 1 wherein said means for determining a
first operating parameter error value as a function of said first
and second engine positions relative to said reference engine
position is further operable to determine a second operating
parameter error value also as a function of said first and second
engine positions relative to said reference engine position.
7. The apparatus of claim 6 wherein said means for sensing a
pressure associated with a fuel system of an internal combustion
engine includes means for sensing fuel pressure of a fuel
collection unit and producing said pressure signal corresponding
thereto, said pressure signal having peak values corresponding to
peak pressures of said fuel within said fuel collection unit;
and wherein said first operating parameter error value corresponds
to an overall system bandwidth and said second operating parameter
error value corresponds to an engine static timing error associated
with a system for controlling operation of said internal combustion
engine.
8. The apparatus of claim 6 wherein said means for sensing a
pressure associated with a fuel system of an internal combustion
engine includes means for sensing pressure of a combustion chamber
of said internal combustion engine and producing said pressure
signal corresponding thereto, said pressure signal having peak
values corresponding to peak pressures within said combustion
chamber;
and wherein said first operating parameter error value corresponds
to an overall system bandwidth and said second operating parameter
error value corresponds to a combined engine static timing error
associated with a system for controlling operation of said internal
combustion engine and a fuel pump phasing error associated with
said fuel system.
9. The apparatus of claim 1 further including means responsive to
said first and second engine positions for determining first and
second offset values corresponding to differences between
respective ones of said first and second engine positions and said
reference engine position, said first operating parameter error
value being a function of said first and second offset values.
10. The apparatus of claim 9 wherein said first operating parameter
error value corresponds to an overall system bandwidth.
11. The apparatus of claim 9 wherein said means for sensing a
pressure associated with a fuel system of an internal combustion
engine includes means for sensing fuel pressure of a fuel
collection unit and producing said pressure signal corresponding
thereto, said pressure signal having peak values corresponding to
peak pressures of said fuel within said fuel collection unit.
12. The apparatus of claim 11 wherein said first operating
parameter error value includes a combined engine static timing
error associated with a system for controlling operation of said
internal combustion engine and a fuel pump phasing error associated
with said fuel system.
13. The apparatus of claim 9 wherein said means for sensing a
pressure associated with a fuel system of an internal combustion
engine includes means for sensing a pressure of a combustion
chamber of said internal combustion engine and producing said
pressure signal corresponding thereto, said pressure signal having
peak values corresponding to peak pressures within said combustion
chamber.
14. The apparatus of claim 13 wherein said first operating
parameter error value includes an engine static timing error
associated with a system for controlling operation of said internal
combustion engine.
15. Apparatus for determining errors in monitored operating
parameters of a fuel system for an internal combustion engine,
comprising:
a pressure sensor for sensing a pressure associated with a fuel
system of an internal combustion engine and producing a pressure
signal corresponding thereto, said pressure signal having peak
values corresponding to peak pressures thereof;
means for determining a reference position of said internal
combustion engine and producing a reference position signal
corresponding to; and
a control circuit responsive to said pressure signal for
determining a first engine position at which a peak value of said
pressure signal occurs, said control circuit determining an
operating parameter error value as a function of said first engine
position relative to said reference engine position.
16. The apparatus of claim 15 wherein said means for determining a
reference engine position and producing a reference engine position
signal corresponding thereto includes an engine position sensor
operable to produce position signal indicative of a predefined
engine position;
and wherein said control circuit is responsive to said position
signal to determine said reference engine position as an engine
position relative to said predefined engine position at which a top
dead center (TDC) position associated with a fuel pump of said fuel
system occurs.
17. The apparatus of claim 15 further including means for
correcting said pressure signal relative to said reference position
signal based on said operating parameter error value.
18. The apparatus of claim 15 wherein said control circuit is
responsive to said first engine position to determine an offset
value corresponding to a difference between said first engine
position and said reference engine position, said operating
parameter error value being a function of said offset value.
19. The apparatus of claim 18 wherein said operating parameter
error value corresponds to an overall system bandwidth.
20. The apparatus of claim 19 wherein said pressure sensor is
operable to sense a fuel pressure of fuel within a fuel collection
unit and producing said pressure signal corresponding thereto, said
pressure signal having peak values corresponding to peak pressures
of fuel within said fuel collection unit;
and wherein said operating parameter error value corresponds to a
combined engine static timing error associated with a system for
controlling operation of said internal combustion engine and a fuel
pump phasing error associated with said fuel system.
21. The apparatus of claim 19 wherein said pressure sensor is
operable to sense a pressure within a combustion chamber of said
internal combustion engine and producing said pressure signal
corresponding thereto, said pressure signal having peak values
corresponding to peak pressures within said combustion chamber;
and wherein said operating parameter error value corresponds to an
engine static timing error associated with a system for controlling
operation of said internal combustion engine.
22. A method of determining errors in monitored operating
parameters of a fuel system for an internal combustion engine, the
method comprising the steps of:
sensing a pressure associated with a fuel system of an internal
combustion engine and producing a pressure signal having peak
values corresponding to peak pressures thereof;
sensing a reference position associated with the operation of said
internal combustion engine;
determining an offset value as a difference between an engine
position at which peak values of said pressure signal occur and
said reference engine position; and
determining an operating parameter error value as a function of
said offset value.
23. The method of claim 22 wherein said operating parameter error
value corresponds to an overall system bandwidth.
24. The method of claim 22 wherein the step of sensing a pressure
associated with a fuel system of an internal combustion engine
includes sensing a pressure of a combustion chamber of said
internal combustion engine, said pressure signal having peak values
corresponding to peak pressures within said combustion chamber;
and wherein said operating parameter error value corresponds to an
engine static timing error associated with a system for controlling
operation of said internal combustion engine.
25. The method of claim 22 further including the step of correcting
said pressure signal relative to said reference engine position
based on said operating parameter error value.
26. The method of claim 22 wherein the step of sensing a pressure
associated with a fuel system of an internal combustion engine
includes sensing a fuel pressure of a fuel collection unit, said
pressure signal having peak values corresponding to peak pressures
of fuel within said collection unit;
and wherein said operating parameter error value corresponds to an
engine static timing error associated with a system for controlling
operation of said internal combustion engine.
27. The method of claim 26 wherein said operating parameter error
value further includes a fuel pump phasing error associated with
said fuel system.
Description
FIELD OF THE INVENTION
The present invention relates generally to systems and techniques
for controlling the operation of an internal combustion engine, and
more specifically to such systems wherein the efficacy of such
control is based on the accuracy of fuel system related operating
parameters.
BACKGROUND OF THE INVENTION
Modern high pressure fuel systems for internal combustion engines
typically employ sophisticated control techniques for monitoring
and controlling multiple fuel system operating parameters
including, for example, fuel supply pressure, injection pressure,
engine timing, rate shape, injected fueling, and the like. However,
even with such advanced control techniques, engine-to-engine
(between-engine) variations are known to exist in at least some of
the typically monitored fuel system operating parameters. For
example, many high pressure fuel and/or engine control systems are
sensitive to between-engine variations in engine static timing and
pump phasing as well as overall system bandwidth. For purposes of
the present invention, an engine static timing error is defined as
any difference between a measured engine reference position (e.g.,
top-dead-center or TDC) and the actual reference position, which
may vary from engine to engine, and a fuel pump phasing error is
defined as any difference between a fuel pump reference position
and a corresponding engine reference position.
As one particular example of the foregoing problem, engine static
timing errors are known to be a significant contributor to
variations in start-of-injection (SOI) in known fuel control
systems. As another example, although accurate fuel supply pressure
sensors and engine position sensors are widely used in high
pressure fuel control systems, such between-engine variations
typically exist with regard to the placement of peak supply
pressures relative to a reference engine position. More
specifically, fuel pumps in cyclic, high pressure fuel control
systems would typically be controlled such that fuel supply
pressure peaks are expected to occur at some predefined crank angle
relative to a reference crank angle (e.g., top-dead-center or TDC)
for each cylinder at a given engine speed. However, due to
between-engine variations in engine static timing and fuel pump
phasing, such fuel supply pressure peaks have been found to deviate
from the predefined crank angle by fixed amounts or offsets from
engine to engine. Similarly, due to between-engine variations in
overall system bandwidth, such fuel supply pressure peaks have also
been found to deviate from the predefined crank angle by variable
amounts as a function of engine speed.
Minimizing such variations by conventional mechanical means
requires tightening tolerances or system specifications, both of
which typically result in increased system cost. What is therefore
needed is a strategy for quantifying and compensating for
between-engine variations in engine static timing and fuel pump
phasing and overall system bandwidth that does not require
additional hardware components and generally does not increase
system cost. Ideally, such a strategy should further provide for
more accurate fuel system operating parameter monitoring and
control, and further provide for improved diagnostic
capabilities.
SUMMARY OF THE INVENTION
The foregoing shortcomings of the prior art are addressed by the
present invention. In accordance with one aspect of the present
invention, an apparatus for determining errors in monitored
operating parameters of a fuel system for an internal combustion
engine comprises means for sensing a pressure associated with a
fuel system of an internal combustion engine and producing a
pressure signal corresponding thereto, the pressure signal having
peak values corresponding to peak pressure values thereof, means
for sensing a reference position of the internal combustion engine
and producing a reference position signal corresponding thereto,
means for determining first and second engine positions at which
peak values of the pressure signal occur at first and second engine
speeds, and means for determining a first operating parameter error
value as a function of the first and second engine positions
relative to the engine position.
In accordance with another aspect of the present invention, an
apparatus for determining errors in monitored operating parameters
of a fuel system for an internal combustion engine comprises a
pressure sensor for sensing a pressure associated with a fuel
system of an internal combustion engine and producing a pressure
signal corresponding thereto, wherein the pressure signal has peak
values corresponding to peak pressures thereof, an engine position
sensor producing a reference position signal corresponding to a
reference position of the internal combustion engine, and a control
circuit responsive to the pressure signal for determining a first
engine position at which a peak value of the pressure signal
occurs. The control circuit is further operable to determine an
operating parameter error value as a function of the first engine
position relative to the reference engine position.
In accordance with a further aspect of the present invention, a
method of determining errors in monitored operating parameters of a
fuel system for an internal combustion engine comprises the steps
of sensing a pressure associated with a fuel system of an internal
combustion engine and producing a pressure signal having peak
values corresponding thereto, sensing a reference position
associated with the operation of the internal combustion engine,
determining an offset value as a difference between an engine
position at which peak values of the pressure signal occur and the
reference engine position, and determining an operating parameter
error value as a function of the offset value.
One object of the present invention is to provide a strategy for
determining engine static timing errors and overall system
bandwidth.
Another object of the present invention is to provide such a
strategy for determining engine static timing, high pressure fuel
pump phasing and overall hydro-mechanical system bandwidth errors
relating to a fuel control system of an internal combustion
engine.
These and other objects of the present invention will become more
apparent from the following description of the preferred
embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A is a diagrammatic illustration of one embodiment of a fuel
control system for an internal combustion engine, in accordance
with the present invention.
FIG. 1B is a diagrammatic illustration of an alternate embodiment
of a fuel control system for an internal combustion engine, in
accordance with the present invention.
FIG. 1C is a diagrammatic illustration of another alternate
embodiment of a fuel control system for an internal combustion
engine, in accordance with the present invention.
FIG. 2 is composed of FIGS. 2A, 2B and 2C wherein each figure
represents a diagrammatic illustration of three distinct
embodiments of an error calculation block forming part of the
control computer illustrated in any one or more of FIGS. 1A-1C, in
accordance with the present invention.
FIG. 3 is a flowchart illustrating one embodiment of a software
algorithm for carrying out the concepts of the present
invention.
FIG. 4 is a plot of cyclic fuel pressure vs. crank angle during
motoring conditions illustrating the general shape of the fuel
pressure peaks under such operating conditions.
FIG. 5 is a plot of cyclic fuel pressure vs. crank angle during
positive fueling conditions illustrating the shape of the fuel
pressure peaks in contrast to those of FIG. 4.
FIG. 6 is a plot of one of the fuel pressure peaks of FIG. 4 with a
curve-fitted estimate thereof superimposed thereon.
FIG. 7 is a plot of one of the fuel pressure waveforms of FIG. 4
illustrating an offset in the waveform due to a limitation in the
overall system bandwidth.
FIG. 8 is a plot of three of the fuel pressure waveforms of FIG. 4,
each representative of a separate physical engine of the same type,
illustrating potential offsets in the peak pressure measurements
thereof due to corresponding variations in engine static timing and
fuel pump phasing.
FIG. 9 is a diagrammatic illustration of one preferred application
of the concepts of the present invention as they relate to a fuel
control strategy including a closed-loop fuel injection quantity
estimation technique.
FIG. 10 is a diagrammatic illustration of one preferred embodiment
of the fuel injection quantity estimation block of FIG. 9.
FIG. 11 is a diagrammatic illustration of one preferred embodiment
of the total discharged fuel estimate block of FIG. 10 including a
bandwidth error and engine static timing/fuel pump phasing error
minimization control technique, in accordance with the present
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
For the purposes of promoting an understanding of the principles of
the invention, reference will now be made to preferred embodiments
illustrated in the drawings and specific language will be used to
describe the same. It will nevertheless be understood that no
limitation of the scope of the invention is thereby intended, such
alterations and further modifications in the illustrated
embodiments, and such further applications of the principles of the
invention as illustrated therein being contemplated as would
normally occur to one skilled in the art to which the invention
relates.
Referring now to FIG. 1A, one preferred embodiment of an electronic
fuel control system 50, in accordance with the present invention,
is shown. Fuel control system 50 includes a source of fuel 52; e.g.
diesel engine fuel, having an inlet port of a fuel pump 54 in fluid
communication therewith. In one embodiment, fuel pump 54 is a high
pressure pump configured to supply high pressure fuel from fuel
supply 52, which may typically be a low pressure fuel supply pump
operable to supply low pressure fuel from a fuel source to fuel
pump 54, to a fuel collection unit 56, in a cyclic fashion, via
supply passage 58. It is to be understood, however, that the
present invention contemplates that pump 54 may alternatively be
configured to supply pressurized fuel in a non-cyclic fashion. In
any case, in the system 50 of FIG. 1A, fuel collection unit 56 is
fluidly connected to a fuel injector 60 via supply passage 62, and
fuel injector 60 is configured to be mounted to an internal
combustion engine 66 in fluid communication with a combustion
chamber thereof as is known in the art. Fuel collection unit 56 may
optionally be fluidly coupled to additional fuel injectors via
supply passage 64. In the embodiment shown in FIG. 1A, the fuel
collection unit 56 is conventionally referred to as a fuel storage
unit, or fuel accumulator.
Central to the electronic control of pump 54 and injector 60 is a
control circuit 68 having a memory unit 75 associated therewith. In
one embodiment, control circuit 68 is a control computer of known
construction, wherein such a circuit 68 is typically referred to by
those skilled in the art as an electronic (or engine) control
module (ECM), engine control unit (ECU) or the like, although the
present invention contemplates that control circuit 68 may
alternatively be any circuit capable of performing the functions
described hereinafter with respect to circuit 68. In any case,
control circuit 68 is operable, at least in part, to control the
fueling of engine 66 in accordance with one or more software
algorithms stored within memory unit 75.
System 50 includes a number of sensors and/or sensor subsystems for
providing control circuit 68 with operational information relating
to some of the components of system 50 as well as certain engine
operating information. For example, fuel collection unit 56
includes a pressure sensor 70 electrically connected to an input
IN1 of control circuit 68 via a number, I, of signal paths 72,
wherein I may be any positive integer. Sensor 70 is preferably a
known sensor operable to sense the pressure of the volume of
pressurized fuel within collection unit 56 and provide a fuel
pressure signal corresponding thereto to input IN1 of control
circuit 68 via signal paths 72, as is known in the art. System 50
further includes an engine speed/position sensor 76 electrically
connected to an input IN2 of control circuit 68 via signal path 78.
In one embodiment, sensor 76 is a known engine speed/position
sensor including a Hall effect sensor disposed proximate to a
toothed gear or wheel rotating synchronously with the crankshaft of
the engine (not shown).
Preferably, the toothed gear or wheel includes a number of
equi-angularly spaced teeth as well as an extra tooth disposed
between adjacent ones of the equi-angularly spaced teeth. Sensor 76
is operable to produce an engine speed/position signal (ES/P)
including information relating to the rotational speed of the
engine crank shaft (not shown) based on the passage thereby of the
equi-angularly spaced teeth, as well as information relating to
engine position relative to a reference engine position (e.g.,
angle of the crank shaft (crank angle) relative to a
top-dead-center (TDC) position of the engine cylinder or combustion
chamber in question) based on passage thereby of the extra tooth.
Alternatively, system 50 may substitute the sensor 76 just
described with one or more known sensors producing equivalent
information in the form of one or more electrical signals.
Control circuit 68 further includes a number of outputs by which
certain components of system 50 may be electronically controlled.
For example, output OUT1 of control circuit 68 is electrically
connected to an actuator 53 of fuel pump 54 via a number, P, of
signal paths 74, wherein P may be any positive integer, and wherein
actuator 53 may be a solenoid or other known actuator. In any case,
actuator 53 of pump 54 is responsive to a pump command signal
produced by control circuit 68 on signal paths 74 to cause the pump
54 to supply fuel from fuel supply 52 to fuel collection unit 56.
Output OUT2 of control circuit 68 is electrically connected to an
actuator 80 (e.g., solenoid) of fuel injector 60 via a number, J,
of signal paths 82, wherein J may be any positive integer, whereby
actuator 80 is responsive to a fuel command signal produced by
control circuit 68 on signal paths 82 to actuate injector 60 to
thereby dispense a quantity of fuel from fuel collection unit 56
into a combustion chamber of engine 66. Actuator 80 further
includes a passageway 81 for directing fuel non-injected fuel from
fuel injector 60 back to fuel source 52 as is known in the art.
It is to be understood that in the embodiment illustrated in FIG.
1A, system 50 may include any number of fuel pumps 54, fuel
collection units 56, fuel injectors 60 and associated passageways
as indicated by the integer designations of signal paths 72, 74, 80
and 90. As one specific example, system 50 configured for a 6
cylinder engine may include a pair of fuel pumps 54, a pair of fuel
collection units 56 and six fuel injectors 60 wherein one fuel pump
54 and associated fuel collection unit 56 is operable to supply
pressurized fuel to a first bank of three fuel injectors (e.g.,
front bank) and the other fuel pump 54 and associated fuel
collection unit 56 is operable to supply pressurized fuel to a
second bank of three fuel injectors (e.g., rear bank). Those
skilled in the art will recognize other combinations of fuel pump
54, fuel collection unit 56, fuel injector 60 and associated
passageways, and that other such combinations are intended to fall
within the scope of the present invention.
Referring now to FIG. 1B, an alternative embodiment of an
electronic fuel control system 50', in accordance with the present
invention, is shown. System 50' is identical in many respects to
system 50 of FIG. 1A, and like reference numbers are therefore used
to identify like components. System 50' of FIG. 1B differs from
system 50 of FIG. 1A in that fuel pump 54 is fluidly connected
directly to a so-called fuel "rail" 92 via supply passage 94,
wherein the fuel rail 92 is fluidly connected to injector 60 and
optionally to a number of additional fuel injectors (not shown). In
one embodiment of the fuel control system 50' illustrated in FIG.
1B, the "fuel collection unit" is comprised of the fuel storage
portion of fuel injector 60, whereby a pressure sensor 96 suitably
located relative to injector 60 is electrically connected to input
IN1 of control circuit 68 via a number, N, of signal paths 98 as
shown in phantom in FIG. 1B. In this embodiment, pressure sensor 96
is operable to sense the pressure of fuel within injector 60 and
provide a corresponding number, N, of fuel pressure signals
corresponding thereto, wherein N may be any positive integer.
In an alternative embodiment of the system 50' illustrated in FIG.
1B, the "fuel collection unit", as this term is used hereinabove,
is comprised of the fuel rail 92, wherein a pressure sensor 100
suitably located relative to rail 92 is electrically connected to
input IN1 of control circuit 68 via a number, M, of signals path
102 as shown in phantom in FIG. 1B. In this embodiment, pressure
sensor 100 is operable to sense the pressure of fuel within fuel
rail 92 and provide a corresponding number, M, of fuel pressure
signals corresponding thereto, wherein M may be any positive
integer. It is to be understood that in either embodiment of the
fuel control system 50' of FIG. 1B, any number of fuel pumps 54,
fuel injectors 60 and fuel rails 94 may be provided and fluidly
connected to any desired combinations or groupings of fuel
injectors 60, as described with respect to FIG. 1A, to thereby
accommodate any desired fuel pump/fuel/rail/fuel injector
combinations or groupings. In any case, it should now be readily
apparent that the term "fuel collection unit", as it relates to the
present invention, may be understood to identify any of an
accumulator-type storage unit, such as unit 56 of FIG. 1A, a fuel
rail-type storage unit, such as fuel rail 94, or a fuel
injector-type storage unit, such as the fuel storage portion of
injector 60, and that the term "fuel storage pressure" refers to
the pressure of fuel stored within any of the foregoing fuel
collection units.
Referring now to FIG. 1C, yet another alternative embodiment of an
electronic fuel control system 50", in accordance with the present
invention, is shown. System 50" is identical in many respects to
systems 50 of FIG. 1A and 50" of FIG. 1B, and like reference
numbers are therefore used to identify like components. System 50"
of FIG. 1C differs from systems of FIGS. 1A and 1B in that fuel
pump 54 may be fluidly connected directly to a so-called fuel
"rail" 92 via supply passage 94, or may alternatively be fluidly
coupled thereto via an accumulator-type fuel collection unit (e.g.
fuel collection unit 56 of FIG. 1A), and illustration of these two
alternatives are represented in FIG. 1C as a dashed-line connection
between supply passage 94 and fuel rail 92. For purposes of the
present invention, system 50" of FIG. 1C may or may not include a
fuel supply pressure sensor (e.g., pressure sensor 70, 96 or 100).
However, system 50" preferably includes a cylinder pressure sensor
106 suitably disposed relative to a combustion chamber 104 of
cylinder of engine 66 and electrically connected to input IN1 of
control circuit 68 via a number, I, of signal paths 108 wherein I
may be any positive integer. In this embodiment, pressure sensor
106 is operable to provide a cylinder pressure signal (CP) on
signal path 108 that is indicative of the pressure within the
combustion chamber 104, wherein engine 66 may have any number of
fuel injector 60 and combustion chamber 104 pairs and associated
pressure sensors 106. It is to be understood, however, that the
present invention contemplates other known techniques for computing
or estimating cylinder pressure, and that such other computing or
estimating techniques are intended to fall within the scope of the
present invention.
Engine static timing and fuel pump phasing errors as well as
overall system bandwidth relating to any of systems 50, 50' and 50"
are, in accordance with the present invention, quantified with
respect to engine 66 so that between-engine variations in engine
static timing and fuel pump phasing as well as overall system
bandwidth may be compensated for. For purposes of the present
invention, the term "overall system bandwidth" is defined as any
single one or combination of a pneumatic, mechanical, hydraulic or
electrical system that contributes to the operating bandwidth of
monitored pressure, wherein the term "monitored pressure" is
defined for purposes of the present invention as either the fuel
storage pressure monitored by any of the sensors 70, 96 and/or 100,
or the cylinder pressure monitored by sensor 106. In any case, it
is known that the phase delay of a system, such as with the various
fuel systems illustrated in FIGS. 1A-1C, varies with operating
frequency (i.e., engine speed), but that engine static timing and
fuel pump phasing errors do not. Using these relationships, a
engine static timing error and a fuel pump phasing error, as well
as overall system bandwidth, are measured, in accordance with the
present invention, by monitoring certain features of the cyclic
fuel supply or combustion chamber pressure signals relative to
engine position (e.g., crank angle) for at least two different
engine speeds (preferably during motoring conditions as will be
described more fully hereinafter), and then back-calculating the
desired parameter values using this information according to a
frequency response model. In one embodiment, for example with
respect to either system 50 of FIG. 1A or system 50' of FIG. 1B,
control circuit 68 is operable to monitor the cyclically varying
pressure of the fuel collection unit (i.e., via pressure sensor 70,
96 or 100) for at least two different engine speeds, determine an
engine position (e.g., crank angle) relative to a reference engine
position at which the fuel pressure peaks occur for each engine
speed, and determine therefrom the system bandwidth and combined
engine static timing and pump phasing errors. This arrangement is
shown in block diagram form in FIG. 2A which shows control circuit
68 receiving as input signals the fuel pressure signal on signal
path 72, 98 or 102 and the engine speed/position signal ES/P on
signal path 78, and including an error calculation block 180
producing as outputs a first system bandwidth value BW1 and a
combined engine static timing and fuel pump phasing error value
(ST+FPP), wherein the first system bandwidth value BW1 is dependent
upon the fuel system itself, operation of the fuel collection unit
and fuel pressure sensor and other hardware associated with control
circuit 68.
In an alternate embodiment, fuel pump phasing errors can be avoided
(i.e., fuel pump phasing errors are bypassed) if combustion chamber
pressure is used in lieu of fuel collection unit pressure in the
calculations. In this embodiment, for example with respect to
system 50" of FIG. 1C, control circuit 68 is operable to monitor
the cyclically varying combustion chamber pressure or cylinder
pressure signal (CP) on signal path 108 for at least two different
engine speeds (wherein the fuel pressure supplied by the fuel
collection unit may be either cyclic or noncyclic), determine an
engine position (e.g., crank angle) relative to a reference engine
position at which the cylinder pressure peaks occur for each engine
speed as before, and determine therefrom a second overall system
bandwidth that is different from the first overall system bandwidth
value BW1, and the engine static timing error that is identical to
the engine static timing error ST described with respect to FIG.
2A. This arrangement is shown in block diagram form in FIG. 2B
which shows control circuit 68 receiving as input signals the
cylinder pressure signal on signal path 108 and the engine
speed/position signal ES/P on signal path 78, and an error
calculation block 180' producing as outputs a second system
bandwidth value BW2 that is different from the first system
bandwidth value BW1, and the engine static timing error value ST
(identical to ST of FIG. 2A). The second bandwidth value BW2, as
compared with BW1, is a function of engine operation, the operation
of the cylinder pressure sensor 108 and other hardware associated
with control circuit 68.
In another alternate embodiment, all of the above information can
be individually obtained by combining the information available in
system 50 and/or 50' with the information available in system 50".
In this embodiment, control circuit 68 is operable to monitor the
fuel pressure signal on signal path 72, 98 and/or 102 as well as
the cylinder pressure signal (CP) on signal path 108 for at least
two different engine speeds, determine an engine position (e.g.,
crank angle) relative to a reference engine position at which the
corresponding pressure peaks occur for each engine speed as before,
and determine therefrom the first and second system bandwidth
values, BW1 and BW2, that are identical to the bandwidth values BW1
and BW2 described with respect to FIGS. 2A and 2B respectively, the
engine static timing error (ST) as described with respect to FIG.
2B, and the combined engine static timing and fuel pump phasing
error (ST+FPP) as described with respect to FIG. 2A. Having the
combined engine static timing and fuel pump phasing error value
(ST+FPP) and the engine static timing error value ST, control
circuit 68 may accordingly compute the individual fuel pump phasing
error FPP as a difference thereof. This arrangement is shown in
block diagram form in FIG. 2C which shows control circuit 68
receiving as input signals the fuel pressure signal on signal path
72, 98 and/or 102, the cylinder pressure signal on signal path 108
and the engine speed/position signal ES/P on signal path 78, and an
error calculation block 180" producing as individual outputs the
first and second system bandwidth values BW1 and BW2, the engine
static timing error value ST and the fuel pump phasing error value
FPP.
Referring now to FIG. 3, a flowchart is shown illustrating a
software algorithm 110 that is preferably stored within memory 75
of control circuit 68, and is executable by control circuit 68 in
order to carry out at least some of the concepts of the present
invention. Algorithm 110 begins at step 112, and at step 114,
control circuit 68 is operable to determine a peak pressure and
corresponding engine position at a first engine speed E1. In one
embodiment, for example with reference to system 50 of FIG. 1A or
system 50' of FIG. 1B, the term "peak pressure" is defined as a
peak pressure of fuel within the fuel collection unit (e.g., fuel
storage unit 56, fuel rail 94 or fuel injector 60) as determined in
accordance with the cyclic fuel pressure signal produced by an
associated pressure sensor (e.g., sensor 70, 96 or 100). In an
alternate embodiment, for example with reference to system 50" of
FIG. 1C, the term "peak pressure" is defined as a peak cylinder
pressure within combustion chamber 104 as determined in accordance
with the cyclic cylinder pressure signal produced by pressure
sensor 106.
In either case, the present invention contemplates a number of
techniques for determining the peak pressure value in step 114. In
one embodiment of step 114, for example, control circuit 68 is
operable to sample an appropriate pressure signal as described
above, as well as engine position, preferably in terms of crank
angle relative to a predefined engine position (e.g.,
top-dead-center or TDC position of the cylinder/combustion chamber
in question) via engine speed/position sensor 76, and compute an
estimating function relating the two parameters. As one example,
control circuit 68 may be operable at step 114 to determine a
second order curve fitting equation such as y=a+bx+cX.sup.2,
wherein y=pressure samples, x=engine position samples, and a, b and
c represent curve fit coefficients, and wherein control circuit 68
is preferably operable to determine the coefficients a, b and c
according to a known recursive or non-recursive least-squares curve
fitting technique. It has been determined through experimentation
that sampling the pressure waveform throughout a 90 crank degree
window with a two crank degree sampling interval, for example,
provides for acceptable parameter identification with the least
squares technique. For example, referring to FIG. 6, a plot of fuel
pressure (e.g., provided by any of the pressure sensors 70, 96 or
100) vs. engine position 128 is shown along with an estimated fuel
pressure function 130 superimposed over curve 128, wherein function
130 was determined in accordance with a second order curve fitting
equation as just described. It is to be understood, however, that
the present invention contemplates that other known functions may
be used in place of the second order equation, and that other known
techniques may be used in place of the recursive or non-recursive
least squares technique for finding the function coefficients, and
those skilled in the art will recognize that such alternate
functions and/or curve fitting techniques are intended to fall
within the scope of the present invention. Having determined an
estimate of the pressure function in accordance with any of the
foregoing techniques, control circuit 68 is thereafter operable to
determine a peak point of the estimated pressure function by
computing the first derivative of the estimation function, equating
it to zero and solving for engine position [e.g., in the above
example, dy/dx=b+2cx=0; x=-b/(2*c)].
As one alternative to the foregoing technique for executing step
114 of algorithm 110, control circuit 68 may be operable at step
114 to determine the peak pressure value by sampling an appropriate
pressure signal as described above at a high sampling rate, and
determining the peak pressure value (and corresponding engine
position) as the zero slope point thereof according to well known
techniques therefore. As another alternative, control circuit 68
may be operable at step 114 to determine the peak pressure value by
computing two first-order linear equations to fit the data; one
equation for pressure/engine position data prior to the peak and
one equation for pressure/engine position after the peak, and
determining the peak pressure value (and corresponding engine
position) as the intersection point thereof. Those skilled in the
art will recognize other known techniques for determining peak
pressure values and corresponding engine positions for the
monitored pressure and engine position signals, and that such other
known techniques are intended to fall within the scope of the
present invention.
Regardless of the technique used in step 114 for determining
pressure peak and corresponding engine position values, sampling of
an appropriate pressure signal, as described hereinabove, and the
engine position signal is preferably carried out during motoring
conditions; i.e., engine and vehicle speed greater than zero under
zero fueling conditions. Under such conditions, as illustrated in
FIG. 4, the pressure signal 124 (e.g., here the fuel pressure
signal provided by pressure sensor 70, 96 or 100) is substantially
sinusoidal about the peak pressures. By contrast, as illustrated in
FIG. 5, the pressure signal 126 (e.g., here also the fuel pressure
signal provided by pressure sensor 70, 96 or 100) under positive
fueling conditions (e.g., here 125 mm.sup.3 /stroke) is not
sinusoidal about the pressure peaks, and determination of the peak
pressure values is accordingly more difficult, particularly by
using any of the simpler known curve-fitting techniques. Those
skilled in the art will recognize, however, that such signal
sampling only during motoring conditions is not strictly required,
particularly when using non curve-fitting techniques for
determining peak pressure values, and that the scope of the present
invention accordingly includes sampling appropriate pressure and
engine position signals during non-motoring conditions.
In any case, execution of algorithm 110 advances from step 114 to
step 116 where control circuit 68 is operable to determine a peak
pressure value and corresponding engine position at a second engine
speed E2 different from engine speed E1. In accordance with the
present invention, control circuit 68 is operable at step 116 to
determine the peak pressure value and corresponding engine position
at E2 in accordance with any of the techniques described
hereinabove with respect to the execution of step 114. In executing
steps 114 and 116, the monitored pressure signal, as this term is
defined hereinabove, is preferably sampled and processed to
determine pressure peaks as described hereinabove during steady
state engine operating conditions during motoring at a first engine
speed (step 114). At a second engine speed that is preferably
displaced from the first engine speed by at least a desired speed
amount, the monitored pressure signal is again sampled and
processed to determine pressure peaks thereat as described
hereinabove (step 116). The first and second engine speeds may, in
accordance with the present invention, occur during the same or
different vehicle motoring events. Alternatively, control circuit
68 may be configured to sample the monitored pressure signal during
any and/or all vehicle motoring events, and subsequently process
such information that was collected at sufficiently different
engine speeds to provide the peak pressure information. Generally,
such data taken at more than two engine speeds tends to improve
accuracy, decrease noise and facilitate the ability to estimate
errors associated with the calculations.
From step 116, the execution of algorithm 110 advances, in one
embodiment, to step 118 where control circuit 68 is operable to
calculate the overall system bandwidth and combined engine static
timing and fuel pump phasing errors as a function of the pairs of
peak pressure values and corresponding engine position values
determined at steps 114 and 116. This particular embodiment is
applicable to systems such as system 50 of FIG. 1A and system 50'
of FIG. 1B, wherein the peak pressure values determined in steps
114 and 116 correspond to fuel pressure peak values based on fuel
pressure signals provided by sensor 70, 96 or 100. At step 118,
control circuit 68 is operable to determine the distances between
the engine positions at which the peak pressure points occurred at
steps 114 and 116 and a reference engine position. In one
embodiment, the reference engine position corresponds to an engine
position at which a top-dead-center (TDC) position of fuel pump 54
occurs. For example, in one known fuel control system, fuel pump
TDC is designed to occur 20 crank degrees after engine TDC, and in
this case, the reference engine position at step 118 corresponds to
engine TDC+20 crank degrees. In this embodiment, control circuit 68
is operable to determine a pair of offset values offset1 and
offset2, wherein offset1 corresponds to a difference between the
engine position at which peak pressure occurs for engine speed ES1
(step 114) and the reference engine position, and offset2
corresponds to a difference between the engine position at which
peak pressure occurs for engine speed ES2 (step 116) and the
reference engine position. Those skilled in the art will recognize
that any engine reference position may be used in step 118 as long
as this engine reference position is subsequently related to an
engine position at which fuel pump TDC occurs in the calculation of
offset1 and offset2, and that such other reference engine positions
are intended to fall within the scope of the present invention.
In any case, if the overall system bandwidth is infinite, and
assuming negligible hydraulic line delay, and further assuming that
the fuel pump 54 and engine position sensor are perfectly aligned,
then the offset values offset1 and offset2 will be zero. However,
due to factors contributing to a finite overall system bandwidth,
and due to the possibility of engine static timing and/or fuel pump
phasing errors, the peak pressure values determined at steps 114
and 116 may not occur at the same engine positions as the reference
engine position. In accordance with the present invention, the
offset values determined at step 118 are thus related to the engine
static timing and fuel pump phasing errors as well as a combined
hydro-mechanical system phase delay and sensor phase delay
(hereinafter referred to collectively as "phase lag") according to
the equation:
Offset=(engine static timing error+fuel pump phase error)+phase lag
(1),
wherein the engine static timing error and fuel pump phase error
represent a fixed, constant error value (hereinafter "ERR") at all
operating conditions of a given engine. In the foregoing equation,
the phase lag varies with input signal frequency of the pressure
signal and the overall system bandwidth, and in one known fuel
system, the frequency of the pressure signal (in units of Hz) is,
for example, 1/40.sup.th of the engine speed (in units of RPM). The
phase lag thus varies with system bandwidth and engine speed. Those
skilled in the art will recognize that other systems may exhibit
different relationships between pressure and engine speed, and that
such different relationships may be substituted into equation (1)
as required. In any case, the phase lag term in the foregoing
equation is preferably modeled as a function of the bandwidth of
the overall system and of the frequency of the pressure signal
provided by any of sensors 70, 96 or 100. For example, in one
embodiment, the overall system frequency response is modeled in
accordance with an ideal first order linear dynamic system, such
that the phase lag may be represented by the equation:
wherein W is the known frequency (Hz) of the pressure signal (e.g.,
engine speed/40), W.sub.P (in units of Hz) is the bandwidth of the
overall system, and K represents a ratio of fuel pump speed to
engine speed (e.g., K=1.5 in one embodiment), and is therefore a
known constant. Substituting equation (2) into equation (1), and
duplicating the equation for the two offset values offset1 and
offset2, leads to the following system of equations:
Offset1=ERR+arctan(W.sub.1 /W.sub.P)/K
wherein W.sub.1 and W.sub.2 (both in units of Hz) are related to
engine speed values ES1 and ES2 (both in units of RPM) such as by
the example given above (e.g., W.sub.1 =ES1/40 and W.sub.2
=ES2/40). Returning again to FIG. 2, control circuit 68 is thus
operable to complete step 118 by solving the two equations (3) for
the two unknowns (ERR and W.sub.P).
In an alternative embodiment of algorithm 110, step 116 advances to
step 120 (shown in phantom) rather than to step 118 where control
circuit 68 is operable to calculate the overall system bandwidth
and the engine static timing error as a function of the pairs of
peak pressure values and corresponding engine position values
determined at steps 114 and 116. This particular embodiment is
applicable to systems such as system 50" of FIG. 1C wherein the
peak pressure values determined in steps 114 and 116 correspond to
cylinder (i.e., combustion chamber) pressure peak values based on
pressure signals provided by sensor 106. In such a case, as
described hereinabove, by using cylinder pressure in the above
equations, fuel pump phasing errors do not enter into the offset
calculations and an engine static timing error alone can thus be
determined. Control circuit 68 is preferably operable to execute
step 120 in an identical manner to that described hereinabove with
respect to step 118, except that ERR=engine static timing only.
Accordingly, the system of equations (3) become:
Control circuit 68 is operable at step 120 to solve equation (4)
for the two unknowns W.sub.P and engine static timing error.
It is to be understood that although equations (3) and (4) are
described as based on a first-order model having two equations and
two unknowns, the present invention contemplates alternatively
defining equations (3) and/or (4) in accordance with other system
models. For example, equations (3) and (4) may be defined as any
desired multiple-order model (i.e., a "Nth" order model in
general), wherein the monitored pressure must typically be sampled
and processed for at least N+1 different engine speeds. As another
example, equations (3) and (4) may be defined in accordance with a
simple linear function. Such alternative system models are intended
to fall within the scope of the present invention.
Referring now to FIG. 7, one example of a monitored pressure
sampling error associated with a limited overall system bandwidth
is illustrated. Assuming for the purpose of FIG. 7 that value ERR
in either of equations (3) or (4) is zero, fuel pressure waveform
128 represents an actual fuel pressure waveform having a peak
pressure value P.sub.PK that occurs at a crank angle CA1. If the
system bandwidth W.sub.P is infinite, a conventional pressure
sampling algorithm will correctly determine the peak pressure value
as P.sub.PK occurring at a crank angle of CA1. However, if the
overall system bandwidth is not infinite but is instead some finite
value, the pressure waveform 128 will be shifted or offset with
respect to crank angle as shown by the phantom pressure waveform
128', wherein the amount of shift or offset is a function of
bandwidth and engine speed. In this case, a conventional pressure
sampling algorithm will determine the peak pressure value P.sub.PK
as occurring at crank angle CA2. If ERR=zero and W.sub.P is
determined according to equation (3) or (4), the Offset value of
equation (1) may be determined at any engine speed as a function of
the computed overall system bandwidth. This Offset value of
equation (1) may then be used in a conventional pressure sampling
algorithm, in accordance with the present invention, to
appropriately shift the sampling timing and thereby compensate for
the offset in crank angle reading at any engine speed. In this way,
an overall system bandwidth W.sub.P less than infinity (e.g., a
limited system bandwidth) can be compensated for in a conventional
pressure sampling algorithm so that the peak pressure value
P.sub.PK may be correctly matched with crank angle CA1.
Referring now to FIG. 8, an example of a monitored pressure
sampling error associated with a combined engine static timing and
fuel pump phasing error (e.g., system 50 or 50') or with an engine
static timing error alone (e.g., system 50") is illustrated.
Assuming for the purpose of FIG. 8 that the overall system
bandwidth Wp is infinite in either of equations (3) or (4), and
that fuel pressure waveform 128 represents a fuel pressure waveform
of an actual engine having a peak pressure value P.sub.PK that
occurs at a nominal crank angle CA1. If the error value ERR is zero
in equations (3) or (4) for a different engine, a conventional
pressure sampling algorithm will determine the pressure value
P.sub.PK as occurring at crank angle of CA1. However, if the
combined engine static timing and fuel pump phasing error (system
50 or 50') or the engine static timing error alone (system 50") is
non-zero, a conventional pressure sampling algorithm will observe a
crank angle shift as a result of this error and therefore determine
the peak pressure value as P.sub.PK as occurring at a different
crank angle. For example, for an engine exhibiting pressure
waveform 128', a conventional pressure sampling algorithm will
determine the pressure peak P.sub.PK as occurring at a crank angle
CA2 that is less than CA1, and for another engine exhibiting
pressure waveform 128", a conventional pressure sampling algorithm
will determine the pressure peak P.sub.PK as occurring at a crank
angle CA3 that is greater than CA1. In each case, the shift or
offset in crank angle at which peak pressure P.sub.PK occurs a
function of ERR alone and is therefore fixed for a fixed ERR value
for any particular engine. If W.sub.P is infinite, then the Offset
value of equation (1) may be determined strictly as a function of
ERR (e.g., engine static timing error with or without a fuel pump
phasing error contribution). This Offset value of equation (1) may
then be used in a conventional pressure sampling algorithm, in
accordance with the present invention, to appropriately shift the
sampling timing and thereby compensate for the offset in crank
angle and peak pressure reading. In this way, an engine static
timing error with or without an additional fuel pump phasing error
contribution can be compensated for in a conventional pressure
sampling algorithm so that errors attributable to between-engine
variations in the peak pressure value P.sub.PK and corresponding
crank angle relationship can be eliminated or at least
minimized.
From either of steps 118 or 120, the execution of algorithm 110
advances to step 122 where control computer 68 is operable to
direct the error values determined at step 118 or step 120 to one
or more appropriate engine control algorithms. As one example of
step 122, engine static timing errors are known to cause
between-engine variations in start-of-injection (SOI) in many fuel
control systems for internal combustion engines. Reducing and even
minimizing the impact of such engine static timing errors would, in
turn, reduce SOI variations and correspondingly provide for
improved emissions and fuel economy. In accordance with one aspect
of the present invention, step 122 may thus correspond to providing
the engine static timing error value (in cases where this error
value is available by itself) to a fuel control system to thereby
reduce between-engine SOI variations by more closely matching
timing relationships between engine position and other fuel system
parameters such as fuel pressure, fuel pump actuator commands, and
the like, as described to hereinabove with respect to FIG. 8.
As another example of step 122, the combined engine static timing
and pump phasing error as well as the bandwidth error have been
observed to cause between-engine variations in systems for
determining fuel injection quantities. One such system for
determining fuel injection quantities is set forth in detail in
co-pending U.S. application Ser. No. 09/565,010, entitled Fuel
Control System Including Adaptive Injected Fuel Quantity
Estimation, the disclosure of which is incorporated herein by
reference. Referring to FIGS. 9-11, some of the details of the
foregoing system, as they relate to the present invention, are
shown. As part of the Fuel Control System Including Adaptive
Injected Fuel Quantity Estimation application described above, the
control computer 68 of FIGS. 1A or 1B may include the control
strategy set forth in FIG. 9, wherein block 132 is configured to
receive a fuel pressure signal (FP) via signal path 72, an engine
speed and position signal (ES/P) via signal path 78 and a commanded
fuel signal (in terms of an injector on-time signal IOT produced by
control circuit 68 on signal path 82) via signal path 134.
Optionally, fuel injection quantity estimation block 132 may
additionally receive an engine temperature signal via signal path
90. An injected fuel estimate (IFE) value is produced by fuel
injection quantity estimation block 132 and is directed to a
subtractive input of summing node 24 via signal path 136. The fuel
injection quantity estimation block 132 thus serves as a virtual
sensor operable to determine injected fuel quantities based on
certain engine and fuel system related operational parameters.
In the operation of the portion of control circuit 68 illustrated
in FIG. 9, two-dimensional look-up table 14 receives a fuel
pressure signal (FP) via signal line 72 and a desired fuel
injection quantity value (DF) from process block 16 via signal path
18. Table 14 is responsive to the fuel pressure signal and the
desired fuel injection quantity value to produce an initial fueling
command as is known in the art. The fuel injection estimation block
132 is responsive to at least the fuel pressure signal (FP) on
signal path 72, the engine speed/position signal (ES/P) on signal
path 78 and the fueling command signal (injector on-time signal
IOT) on signal path 134 to estimate an injected fuel quantity and
supply a corresponding injected fuel quantity estimate (IFE) to a
subtractive input of summing node 24 via signal path 136. Node 24
produces an error value as a difference between the desired fuel
injection quantity (DF) and the injected fuel quantity estimate
(IFE) and applies this error value to a controller 26. Controller
26 is responsive to the error value to determine a fuel quantity
adjustment value, wherein the initial fueling command and the fuel
quantity adjustment value are applied to additive inputs of a
second summing node 28. The output of summing node 28 is an output
82 of control circuit 68 that represents a final fueling command,
wherein the final fueling command is the initial fueling command
produced by table 14 adjusted by the fuel quantity adjustment value
produced by controller 26.
Referring now to FIG. 10, an embodiment of the fuel injection
quantity estimation block 132 of FIG. 9 is shown. Block 132
includes a total discharged fuel estimate block 140 receiving the
fuel pressure signal (FP) via signal path 72 and the engine
speed/position signal (ES/P) via signal path 78. Optionally, as
shown in phantom in FIG. 10, block 140 may be configured to receive
the engine or fuel temperature signal (ET) via signal path 90. In
any case, block 140 is operable, as will be more fully described
hereinafter, to process at least the fuel pressure (FP) and engine
speed/position (ES/P) signals and produce a total discharged fuel
estimate value (TDFE) on signal path 144 corresponding to an amount
of pressurized fuel removed from the fuel collection unit 56
pursuant to a fuel injection event.
Fuel injector control actuator 80 of fuel injector 60 is controlled
by control circuit 68 to direct or spill at least some of the
pressurized fuel supplied by fuel collection unit 56 to fuel
injector 60 back to fuel supply 52 via a hydraulic path or fuel
passageway 81 in order to cause an actual fuel injection event to
occur, as is known in the art. In such cases, the fuel injection
quantity estimation block 132 of the present invention accordingly
includes a control flow leakage estimate block 146 operable to
estimate such a fuel spill amount, as will be described more fully
hereinafter, so that the fuel spill amount can be subtracted from
the total discharged fuel estimate value (TDF) in determining the
injected fuel estimate (IFE). The fuel pressure signal (FP) on
signal path 72 and the final fueling command (in terms of injector
on-time IOT) on signal path 134 are provided to the control flow
leakage estimate block 146 which is operable to process these
signals and produce a control flow leakage estimate value (CFLE) on
signal path 148. Optionally, as shown in phantom in FIG. 5, one or
more additional signals may be supplied to block 146 via signal
path 187, wherein block 146 is operable to process such signals
along with the IOT and FP signals to produce the control flow
leakage estimate (CFLE). Examples of signals available on signal
path 187 include, but are not limited to, engine speed/position,
engine timing, and the like. As a further option, block 146 may be
configured to receive the engine or fuel temperature signal (ET)
via signal path 90. In any case, signal path 144 is supplied to an
additive input of a summing node 142, and signal path 148 is
supplied to a subtractive input of summing node 142. An output of
summing node 142 forms the output 136 of the fuel injection
quantity estimation block 132 and accordingly carries the injected
fuel estimate value (IFE).
Those skilled in the art will recognize that the control flow
leakage estimate block 146 is necessarily included in fuel systems
having so-called indirect control (e.g., injectors defining a
hydraulic link between the injector inlet port and outlet drain)
over fuel injector delivery time or "on-time" as this term is used
herein. Conversely, it should also be recognized that fuel systems
are known that include structure providing for direct control over
fuel injector delivery time or on-time. In these types of fuel
systems, spill valves of the type just described are therefore
unnecessary and no control flow exists to create an actual
injection event. In such systems, the control flow leakage estimate
block 146 can therefore be omitted.
Optionally, as shown in phantom in FIG. 10, the fuel injection
quantity estimation block 132 may include a parasitic flow leakage
estimate block 150 receiving the fuel pressure signal (FP) and
engine speed/position signal (ES/P) via signal paths 72 and 78,
respectively. Additionally, block 150 receives an engine
temperature signal (ET) via signal path 90 and the total discharged
fuel estimate value TDFE on signal path 144 via signal path 152.
Finally, block 150 may be configured to receive one or more
additional signals via signal path 154 as will be more fully
described hereinafter. The parasitic flow leakage estimate block
150 is operable to process the foregoing information and produce a
parasitic flow leakage estimate (PFLE) on signal path 156 which is
supplied to a subtractive input of summing node 142. The injected
fuel estimate (IFE) of block 132 is, in this case, is the total
discharged fuel estimate (TDFE) minus the control flow leakage
estimate (CFLE) and the parasitic flow leakage estimate (PFLE).
In some fueling systems, the parasitic leakage on the injected fuel
and quantity estimate (IFE) may be negligible. In other systems,
non-negligible parasitic leakage levels may be minimized by reading
pre- and post-injection fuel pressure values very close to the
injection event itself. In any such fuel system embodiments wherein
such parasitic leakage may be negligible, the parasitic flow
leakage estimate block 150 may be omitted from the fuel injection
quantity estimation block 132, with the injected fuel estimate
(IFE) then being computed as a difference between the total
discharged fuel estimate (TDFE) and the control flow leakage
estimate (CFLE) in fuel systems having a control flow of fuel as
described above, or simply as the total discharged fuel estimate
(TDFE) in fuel systems having no control flow. In other fuel
systems, the parasitic flow leakage estimate (PFLE) may contribute
significantly to the injected fuel estimate (IFE), in which case
the parasitic flow leakage estimate block 150 should be included
for accuracy. In any case, preferred embodiments and operation of
the parasitic flow leakage estimate block 150 will be more fully
described hereinafter.
Referring now to FIG. 11, one preferred embodiment of the total
discharged fuel estimate block 140 of FIG. 10, in accordance with
the present invention, is shown. Block 140 includes a fuel pressure
sampling algorithm 160 that is responsive to the fuel pressure
signal (FP) on signal path 72 and the engine speed/position signal
(ES/P) on signal path 78 to sample fuel pressure across a fuel
injection event and produce a pre-injection fuel pressure value
(FP.sub.PRE) and a post-injection fuel pressure (FP.sub.POST). The
fuel pressure sampling algorithm 160 is operable to compute
FP.sub.PRE and FP.sub.POST as average fuel pressures over
predefined crank angle windows relative to crank TDC. For example,
in one embodiment algorithm 160 is operable to sample the fuel
pressure signal on signal path 72 every 2 degrees of crank angle,
and to compute FP.sub.PRE as the average of eight fuel pressure
values between -30 to -16 crank angle degrees prior to cylinder
TDC, and FP.sub.POST as the average of eight fuel pressure values
between 46 and 60 crank degrees after cylinder TDC. It is to be
understood, however, that other sampling ranges of any desired
crank angle window can be used to provide the pre- and
post-injection fuel pressure values FP.sub.PRE and FP.sub.POST,
respectively.
Block 140 further includes, in accordance with the present
invention, a bandwidth and engine static timing/fuel pump phasing
error calculation block 180 providing the engine static timing and
fuel pump phasing error value EST/FPP (i.e., the ERR value of
equations (1)-(3)) and bandwidth value BW (i.e., the W.sub.P value)
of equations (2)-(3)) to the fuel pressure sampling algorithm 160.
Block 180 is operable to compute the engine static timing/fuel pump
phasing error value EST/FPP and bandwidth value BW, as described
hereinabove, and provide these error values to algorithm 160 to
improve the accuracy of the fuel pressure sampling algorithm. For
example, these error values may be used, in a known manner, to
improve the timing of the fuel pressure sample values relative to
engine position; i.e., to more accurately match fuel pressure
samples with crank angle values, than was otherwise possible with
algorithm 160 alone, examples of which are described hereinabove
with respect to FIGS. 7 and 8. Doing so provides for more accurate
and consistent between-engine fuel pressure sampling behavior, and
therefore provides for improved accuracy of the fuel injection
quantity estimation block 132 as a whole.
The total discharged fuel estimate block 140 further includes a
fuel discharge estimation block 162 operable to produce a total
discharged fuel estimate (TDFE) on signal path 144 based on the
pre- and post-injection fuel pressure values FP.sub.PRE and
FP.sub.POST. Block 162 preferably comprises a regression equation
that produces the total discharged fuel estimate (TDFE) as a
function of F.sub.PRE and of FP.sub.POST. For example, in this
embodiment, the total discharged fuel estimate value (TDFE) is
computed by block 162 in accordance with the equation
TDFE=a+b*FP.sub.PRE +c*FP.sub.PRE *FP.sub.PRE +d*FP.sub.POST
+e*FP.sub.POST *FP.sub.POST +f*ES/P, wherein a-f are regression
parameters. Those skilled in the art will recognize that the
foregoing regression equation parameters for estimating the total
discharged fuel based at least on fuel pressure values may be
determined using known and common curve-fitting techniques, and
that other curve-fitting equations, model-based equations or other
desired equations that are a function of at least FP.sub.PRE and
FP.sub.POST may be substituted for the foregoing regression
equation for determining TDFE, and that such alternate equations
are intended to fall within the scope of the present invention.
Examples of other curve-fitting techniques, for example, include,
but are not limited to, least squares data-fitting techniques, and
the like. In any case, signal path 144 is the output of block 162
and carries the total discharged fuel estimate (TDFE) produced by
block 140.
In an alternative embodiment, the total discharged fuel estimate
block 140 may be configured to include as part of the total
discharged fuel estimate (TDFE) effects thereon of changes in the
bulk modulus of the fuel contained in the fuel collection unit (as
this term is defined hereinabove). For example, the relationship
between energy stored in the fuel collection unit and the change in
fuel volume is known to be dependent upon the effective bulk
modulus of the system. An estimate of the effective bulk modulus of
the fuel system may thus be used to improve the total discharged
fuel estimate (TDFE) of block 140, and block 140 may therefore
optionally include a pre- and post-injection fuel pressure slope
determination block 166 receiving the individual pre-injection fuel
pressure values FP.sub.PREi and individual post-injection fuel
pressure values FP.sub.POSTi from the fuel pressure sampling
algorithm 160. Optionally, as shown in phantom, block 166 may be
configured to receive the engine or fuel temperature signal (ET)
via signal path 90. In any case, block 166 is operable to determine
in accordance with well-known equations, the slope of the
pre-injection fuel pressure signal during the predefined crank
angle window (SLOPE.sub.PRE) and the post-injection slope of the
fuel pressure signal during the predefined crank angle window
(SLOPE.sub.POST), respectively. The fuel pressure slope values are
then provided to the fuel discharge estimation block 162 wherein
block 162 is configured, in this embodiment, to compute TDFE as a
function of at least FP.sub.PRE, FP.sub.POST, SOPE.sub.PRE and
SLOPE.sub.POST. In one embodiment, for example, fuel discharge
estimation block 163 is operable to compute the discharged fuel
estimate TDFE in accordance with a regression equation of the type
described hereinabove with respect to the previous embodiment of
block 140, wherein at least the values SLOPE.sub.PRE and
SLOPE.sub.POST are used in addition to the values FP.sub.PRE and
FP.sub.POST (e.g., TDFE=a+b*FP.sub.PRE +c*FP.sub.PRE *FP.sub.PRE
+d*FP.sub.POST +e*FP.sub.POST *FP.sub.POST +f*SLOPE.sub.PRE
+g*SLOPE.sub.PRE *SLOPE.sub.PRE +h*SLOPE.sub.POST +i*SLOPE.sub.POST
*SLOPE.sub.POST +j*ES/P, wherein a-j are regression parameters). As
with the previously discussed embodiment of block 162, however,
those skilled in the art will recognize that the foregoing equation
represents a known and common curve-fitting technique, and that
other curve-fitting equations, model-based equations or other
desired equations that are a function of at least FP.sub.PRE,
FP.sub.POST, SLOPE.sub.PRE and SLOPE.sub.POST may be substituted
for the foregoing regression equation for determining TDFE, and
that such alternate equations are intended to fall within the scope
of the present invention. Examples of other curve-fitting
techniques, for example, include, but are not limited to, least
squares data-fitting techniques, and the like. In any case, signal
path 144 is the output of block 162 and carries the total
discharged fuel estimate (TDFE) produced by block 140. Block 166
may additionally be configured to produce an instantaneous bulk
modulus value .beta..sub.i on signal path 163 corresponding to the
instantaneous bulk modulus of the pressurized fuel, a bulk modulus
slope value .beta..sub.s on signal path 165 corresponding to a
slope of the bulk modulus function over a range of fuel pressure
values, a bulk modulus intercept value .beta..sub.I corresponding
to a zero-pressure bulk modulus value of the bulk modulus function
on signal path 169, and a bulk modulus function .beta..
Referring again to FIG. 2, the execution of algorithm 110 advances
from step 122 to step 123 where algorithm 110 is returned to its
calling routine. The present invention recognizes that the
magnitudes of the engine static timing and fuel pump phasing errors
as well as the overall system bandwidth depend upon many factors
and may further vary over time as a function of, for example,
climate, frequency of use, prolonged use, etc. Accordingly,
algorithm 110 is preferably executed at least once per ignition
cycle of the engine 66, although the present invention contemplates
that algorithm 110 may alternatively be executed either more or
less frequently as desired.
While the invention has been illustrated and described in detail in
the foregoing drawings and description, the same is to be
considered as illustrative and not restrictive in character, it
being understood that only preferred embodiments thereof have been
shown and described and that all changes and modifications that
come within the spirit of the invention are desired to be
protected. For example, the concepts of the present invention may
be implemented as an on-line (real-time) technique in an operating
vehicle, as an off-line service or diagnostic feature as part of
normal vehicle/engine service, and/or as part of an engine test
rig. Those skilled in the art will recognize other uses of the
concepts of the present invention, and that such other uses are
intended to fall within the scope of the present invention.
* * * * *